Individuals typically require a comfortable surface, or mattress, on which to recline while sleeping or resting. In particular, individuals involved in activities such as camping and backpacking need a mattress which is portable, lightweight, puncture resistant, inflatable or self-inflatable, insulating, and comfortable. Smaller units may be used as pillows. Further, lightweight portable mattresses find use in many other areas.
Mattresses intended for camping and backpacking have used a number of approaches to obtain these properties. They include: a) basic chambered air mattresses; b) simple thin resilient insulating pads; c) open-cell resilient foam pads (typically 1 to 2 inches thick); and d) a variety of insulated air mattresses.
Each of these approaches has been found deficient in one or more aspects. Basic chambered air mattresses provide very little insulating benefit and require an excessive amount of time and effort to inflate. Thin pads fabricated from natural resilient materials tend to be relatively heavy and provide very little cushioning benefit. Thin pads made from synthetic materials, such as closed-cell vinyl-nitrile (Ensolite), ethylene-vinyl acetate (EVA), or polyethylene foam, reduce weight but provide only a limited comfort benefit. Pads made from thermoformed closed-cell foams are described in U.S. Pat. No. 4,980,936 to Frickland et al. That patent also presents extensive background material on the use of foamed pads. Although closed-cell foam pads could be made thicker, this would increase weight and reduce portability.
Portable pads formed of resilient open-cell foam sheets, such as polyurethane are typically 1.0 to 2.5 inches thick. This resilience and increased thickness makes the pad somewhat more comfortable at the expense of increased weight and bulk.
Thereafter, inventors created several versions of insulated air mattresses. These designs completely or partially filled an air-impervious air mattress cover with resilient insulating materials. One such approach to providing a self-inflating foam filled air mattress is disclosed in U.S. Pat. No. 3,798,686. In this patent the resistance of the foam core to compression is utilized to give the air mattress its self-inflating characteristic. The foam core shown in this patent comprises upper and lower continuous sheets of open-celled foam, between which two layers of crossing foam ribs are configured. The foam components are all bonded to one another, and the entire structure is enclosed within a flexible cover, preferably of an air-impervious nylon type. The limited number of spaced 0.75 inch width rectangular foam ribs on 2.5 inch centers together with stress caused by low superatmospheric pressure, generates higher stress levels at the edge of the bonds than at areas towards the center of each bonding area. This unequal utilization of the ribs' tensile strength properties increases overall weight and the probability of bond delamination or rib tearing beginning at the rib edges and progressing towards the center of each bond. Compensatory measures such as increasing rib or bond strength leads to increased weight and/or costs. This design relies upon the upper and lower continuous sheets of open-cell foam for much of its insulating benefit. When rolled, the areas under the longitudinal (lengthwise) ribs are significantly bulkier than adjacent areas, leading to a greater than necessary overall rolled size.
U.S. Pat. No. 4,688,283 to Jacobson, et. al. discloses a multi-chambered mattress which utilizes an open-cell foam within a air-impervious nylon cover. The mattress is divided along its length into multiple chambers with differing thicknesses of foam. The significant quantity of open-cell foam materials together with the air-impervious cover leads to the weight penalty associated with both of the preceding designs.
U.S. Pat. Nos. 4,025,974 and 4,624,877 to Lea, et al. disclose a single chamber design which encloses a single slab of open-cell foam. The patentees laminate the top and bottom surfaces of an open-cell foam to the inside of a cover made of an air-impervious plastic-coated fabric. This foam-to-cover bond reduces displacement ("ballooning" or "billowing") of the covers and enables better pressure management. Billowing occurs when top and bottom covers are inadequately linked mechanically to each other and are free to expand from one another. Unless it is limited properly, this billowing creates an unstable surface and provides inconsistent support for the user. As with the other self-inflating insulated air-mattresses described above, the use of a solid insulating open-cell foam sheet and separate air-impervious cover components significantly increases mattress weight. Unless done with great care, perforation of the open-cell foam sheet to reduce weight may act to; a) reduce insulation; b) lead to destructive delamination between the foam sheet and the cover element where the remaining foam or bonding area is unable to sustain the load placed upon it; and c) diminish the mattress's horizontal dimensional rigidity. The insulation value of the open-cell foam sheet is critical since the cover does not provide significant insulating value. In U.S. Pat. No. 4,025,974 at Column 10, lines 14-19 and at Column 11, lines 40-47 it is stressed that it is necessary to bond the cover to the foam-sheet along substantially the entire horizontal surface because there is a tendency when a small area of non-bonding bonding or delamination occurs in an area where the skin is tensioned outwardly for this delamination to spread progressively, even under moderate pressure. Given the inflated profile of the cover and open-cell foam sheet when bonded together, perforation of the open-cell foam sheet of U.S. Pat. No. 4,025,974 would accelerate the delamination process. While the bond between the foam and cover could be strengthened through use of an improved adhesive, the necessity of bonding the entire foam surface to the cover could significantly increase cost and weight. Because of the flexible nature of the air-impervious cover, this design relies upon the open-cell foam sheet for the dimensional rigidity necessary for proper inflation. More recent designs have utilized foam sheets with transverse circular perforations or tubular voids running horizontally through the foam sheet. This approach leaves substantially continuous thin foam layers along all of the inside bottom and top mattress covers, inter-connected by foam material or ribs. The thin foam layer imparts the dimensional rigidity necessary to support the cover between adjacent ribs. The ribs are on approximately 2.75 inch centers and are approximately the same width as that of the longitudinal void spaces remaining between the horizontal tubular voids. While the ribs run in only one direction and the fabrication approach differs, this design shares common features with the previously referenced U.S. Pat. No. 3,798,686. The thin layers of foam left at the top and bottom of the foam sheet over the tubular voids increase the relative load bond area resisting delamination at the expense of increased fabrication complexity and expense. While increasing bond area, this approach makes inefficient use of the foam and fabric coating (or adhesive) tensile strength, focusing the greatest stress along the outer edges of each foam rib (and associated bond) and relatively lower stress towards the center of each foam rib.
As additional background information, other examples of foam filled structures are disclosed in the following patents: British Pat. No. 984,604; Brawner U.S. Pat. No. 1,159,166; Nappe U.S. Pat. No. 2,834,970; Lerman U.S. Pat. No. 3,323,151; Cornes U.S. Pat. No. 3,378,864; Kain U.S. Pat. No. 3,537,116; and Gottfried U.S. Pat. No. 3,611,455. In U.S. Pat. No. 4,092,750 a metallized film is used in the mattress's interior for added insulation.
Even with the use of tough coated synthetic fabrics, these mattresses are susceptible to punctures. A foreign object only has to penetrate between fabric strands to puncture the very thin polymer coating. Previous designs have focused upon the use of very thin materials, typically in the range of about 4 mils to about 15 mils. When such a mattress is punctured, air pressure is lost, and the mattress's support is reduced or lost completely.
Finally, the mattress's comfort is limited by the fully sealed nature of the mattress. This limits the mattress's ability to respond to changing conditions, such as switching from lying on one's back to lying on one's side. One example of an attempt to eliminate this limitation is presented in U.S. Pat. No. 4,328,083 to Lineback. This approach locates one or more resilient subchambers within the confines of the larger air mattress envelope. When force is applied to the air mattress, the enclosed fluid presses against the resilient subchambers. Being open to the atmosphere, these chambers deform, releasing air to the atmosphere, thereby partially releasing pressure within the primary chamber. The fixed resilience of these subchambers restrict the ability of the air mattress to respond to individuals with differing weights and to individual preferences.
The present invention overcomes the weight, comfort, and puncture problems associated with prior insulated air mattresses. Relatively thick air-impervious foamed material is used in place of at least one of the prior thin fabric or plastic sheet materials to provide at least one surface which generally is used as the bottom surface of the cover or enclosure. This approach enables one component to provide air-imperviousness, insulating, puncture resistance, and dimensional rigidity functions leading to an overall weight reduction. Weight is further reduced through the use of internal resilient material configurations which provide a high degree of void space. The corresponding decrease in bond area enables the use of stronger bonding agents to bond the resilient materials to the covers without an overall increase in cost. Optionally, bond strength is enhanced through the use of sculptured bonding surfaces to equalize tension across the bond. Optionally, mattress dimensional rigidity may be increased through the configuration of additional separately inflated chambers in the interior of the mattress. Optionally, comfort is enhanced by a configurable subchamber filled with resilient material configured such that the controlled release of internal mattress pressure is enabled when a force is applied to the mattress.
While the prior art has recognized the value of a wide range of design features, in the present invention those properties are utilized in combination and in select configurations to: a) reduce the stored volume of the internal resilient materials; b) maintain reliability as the quantity of resilient material is reduced; c) increase comfort across a broader range of mattress configurations; d) optimize the performance of the relatively thick air-impervious foamed material when used in self-inflating application; e) enhance self-inflation and largely self-inflating operation; and f) reduce overall weight.